a) Field of the Invention
The present invention relates to an integrated optical device, and more particularly to a hybrid type integrated optical device having optical components such as laser diodes, photo-isolators, and photodiodes, respectively integrated on a single substrate.
b) Description of the Related Art
FIG. 16 shows a conventional transceiver for optical communications. A laser diode chip 103 is fixed to a sub-carrier 101, with a heat sink 102 being interposed therebetween. Lenses 105 and 108 are fixed to lens holders 104 and 107. An optical fiber 110 is fixed by an optical fiber holder 111.
A laser beam emitted from a laser diode chip 103 is collimated by the lens 105, passes through an optical member 106 such as a optical-isolator, is converged by the lens 108, and guided to the optical fiber 110.
For the alignment of an optical axis, the sub-carrier 101, lens holders 104 and 107, optical member 106, and optical fiber holder 111 are all placed on a fine positional adjuster to precisely align the optical axes with one another.
This alignment is performed by measuring the intensity of a laser beam emitted from the laser diode chip 103, entered the optical fiber 110, and outputted therefrom. After the optical axis alignment, the holders and carriers are fixed to a substrate 100, for example, by laser welding.
With this method, it is necessary to use an assembly apparatus equipped with a fine adjuster which performs a precise position alignment. It takes a time to finish optical axis alignment. As a result, manufactured optical devices become expensive.
It is difficult to make optical components compact because these components are required to be mounted on the assembly apparatus. It is also necessary to change the structure of the assembly apparatus each time the structure of an optical device is changed. This method therefore is not suitable for manufacturing a small number of, and a variety of, optical devices.
FIG. 17 shows the structure of an integrated optical device eliminating the above disadvantages, as proposed in the Proceedings of the 1992 IEICE Autumn Conference, page4-235.
Lenses 121 and 124 are fitted in lens guide holes 127 and 128 formed on a single crystal silicon substrate 120 to fix the lens positions. As the lens guide holes, via holes may be used which are of an upside-down pyramid shape surrounded by the (1 1 1) planes exposed by anisotropically etching a silicon substrate having the (1 0 0) plane.
In order to eliminate eclipse of a laser beam to be caused at the surface of the substrate 120, laser beam transmitting groves 129, 130, 131, . . . are formed on the surface of the substrate 120 along the optical axes by light assisted etching.
The light assisted etching, which includes the etching technology called laser assisted etching, laser-induced chemical etching, UV light-excited silicon dry etching, and laser ablation, is a method of selectively etching the surface of a substrate only where a high output laser beam such as a YAG laser, argon laser, and excimer laser is applied. With this method, the laser beam transmitting grooves can be formed on the substrate surface by scanning a laser beam along the optical axes.
A filter type prism 126 is fitted in a hole formed on the surface of the silicon substrate 120 so that the prism 126 can be easily aligned in position.
An incident light beam which enters through the groove 131 includes the light beams having wavelength of 1.31 .mu.m and 1.55 82 m. The combined prism 126 splits the incident light beams into 1.31 .mu.m light beam and 1.55 .mu.m light beam. The light beam of 1.55 .mu.m is bented by a plane interference filter formed in the combined prism 126 and launched from the substrate through the groove 132. A portion of the light beam of 1.31 .mu.m is reflected by another plane and travels through the groove 130 and reaches to the photodiode 125. A portion of a light beam emitted from a laser 122 goes through the prism 126 and is launched from the substrate through the groove 131.
Since lenses and the like are aligned in position by forming lens guide holes and the like by anisotropic etching of silicon, complicated optical axis alignment is not necessary.
In the conventional optical device shown in FIG. 17, the substrate surface is etched by light assisted etching to form laser beam transmitting grooves. Therefore, it becomes necessary to scan the substrate surface to be etched by a laser beam or the like.
It is difficult, however, to scan a laser beam at a high speed. It is also necessary to scan a plurality of times in order to obtain a desired etching depth, for example, to obtain a groove of about 50 .mu.m depth shown in FIG. 17. As a result, it takes a long time to work substrates.